Technical Field
The present disclosure relates to wet cleaning processes and equipment and, in particular, to wet cleaning of integrated circuit wafers in the semiconductor industry following chemical-mechanical polishing (CMP).
Description of the Related Art
Wet chemical processing and wet cleaning are frequently executed steps used to fabricate integrated circuits on semiconductor wafers. In particular, various types of wet chemical processes typically are used to etch wafers, to clean wafers following etching, to polish wafers, and to clean wafers following polishing. Wet processing equipment used in all four of these operations generally is designed to include multiple processing modules such as one or more chemical processing modules, one or more water rinse modules, and a wafer dryer. The processes and equipment needed for such wet processing operations are similar in some respects and quite different in other respects.
Some conventional wet chemical wafer cleaning operations entail immersing wafers in a tank, wet chemical processing for etching and associated post-etch cleaning. Typically, batches of wafers or single wafers are held upright in a vertical orientation within immersion tanks during wet processing. Chemical immersion tanks are typically made from non-reactive materials such as, for example, polytetrafluoroethylene (PTFE, known as “teflon”), or stainless steel. Following chemical treatment, wafers can be moved to a separate rinse module such as a water rinse tank, to receive a treatment that arrests chemical reactions occurring on the wafer surface. Water rinse tanks are also used to achieve pH neutralization following exposure of wafers to acidic or basic chemicals during processing in the chemical immersion tanks. Thus, the water tanks are exposed to chemicals used in the steps that precede the pH neutralization step, which means the water tank materials must also be resistant to such chemicals. Spray processing modules are one alternative to immersion tanks for chemical and/or water processing. Spray processing typically entails spraying individual wafers that are held in a horizontal position.
Some chemical immersion tanks and/or water rinse tanks are equipped with a sonic vibration system to assist in removing particles from wafer surfaces by vibrating the water while the wafer is submerged. Once particles are dislodged by the sonic vibrations, the particles can float away from the wafer surface. When the sonic vibration system operates at a vibration frequency in the MHz range, the process is referred to as a “megasonic” clean.
Wafer dryers can use, for example, nitrogen gas and/or a solvent such as isopropyl alcohol (IPA) to evaporate rinse water from the wafers. Additionally or alternatively, a high-speed spinning machine can drive water from the wafers by the action of a centrifugal force.
Single wafers or groups of wafers are typically transported between processing modules by one or more automated transport devices such as industrial manufacturing robots. Such robots can be designed to function in an aqueous environment and/or which may be chemically resistant. Such robots can be single axis, dual axis, or triple axis robots.
Some chemical immersion tanks and/or water rinse tanks are equipped with brushes that assist in removing particles from the wafer surfaces. Brushes are especially useful for removing slurry particles that may remain on the wafer surface after completing a CMP process. Brush cleaning typically entails scrubbing the front side of each individual wafer to remove particulates from at least partially formed integrated circuits.
Typically, neither etching nor post-etch cleaning involves scrubbing wafers with slurry or brushes. On the other hand, existing post-polish wafer cleaning equipment typically uses slurry and brushes combined with water or dilute acidic detergents, as opposed to concentrated chemicals and/or complex sequences of chemicals to clean the wafer. The design of wet cleaning equipment depends in large part on what chemicals are used. For example, the type of chemical to be used in the cleaning system determines the materials allowed for the tanks, delivery lines, hardware, filters, and even soldering methods used to plumb the delivery lines. Furthermore, different types of chemicals can require different safety features that impact equipment design. The design of post-polish cleaning equipment is therefore different from that of post-etch cleaning equipment in that the handling, delivery, and disposal of water and detergents containing particulate slurries will differ significantly from those needed for concentrated corrosive chemicals such as sulfuric acid, ethylene glycol, and the like that are typically used in post-etch cleaning.